Corrosion restraining composition



United States Patent 3,362,912 CORROSION RESTRAINING COMPOSITION Eric Milton Chadwick and Richard Stanley Moreton,

Manchester, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain N0 Drawing. Filed Feb. 1, 1965, Ser. No. 429,611 Claims priority, application Great Britain, Feb. 18, 1964, 6,713/64 11 Claims. (Cl. 252-149) ABSTRACT OF THE DISCLOSURE A corrosion restraining composition which is a mixture of di-n-butylthiourea and a surface active agent obtained by the reaction of an aldehyde with a substituted polynuclear aromatic compound bearing as a substitutent a polyethenoxy chain.

This invention relates to corrosion restraining compositions and more particularly it relates to liquid compositions for restraining the corrosion of ferrous metals in acid pickling baths.

Ferrous metals, such as steel, which are subjected to working at elevated temperatures during the course of manufacture become coated with a layer of oxide impurity, often referred to as mill scale. For many subsequent processing operations, such as coating or plating, it is necessary to remove the layer of oxide scale and it is usual to do this by treating the metal in a bath of aqueous acid, an operation referred to as acid pickling. The acid commonly used for this purpose is sulphuric acid although other acids such as hydrochloric acid, phosphoric acid and sulphamic acid may be used. Once the layer of oxide scale is removed, the acid is free to attack the exposed metal surface and in order to reduce the attack on the metal itself as much as possible it is advantageous to add a corrosion restrainer to the acid pickling bath.

In some cases it is the practice in the industry to recover acid by removal of ferrous sulphate from the spent acid pickling liquors. This can be accomplished by various techniques but where air blowing is used to assist cooling prior to removal of copperas (FeSO -7H O) or where submerged combustion or spray evaporation is used to recover ferrous sulphate monohydrate it is desirable that any additives to the acid pickling process should not give rise to appreciable foam formation at the subsequent acid/iron salt recovery stage.

We have now found that a particularly valuable corrosion-restraining composition for addition to acid pickling baths may be obtained by mixing together di-n-butylthiourea with a surface active agent obtained by reacting a substituted polynuclear aromatic compound bearing as a substituent a polyethenoxy chain with an aldehyde, such surface active agents being more fully described in copending US. patent application No. 344,553.

Thus the invention provides a corrosion restraining composition which comprises a mixture of di-n-butylthiourea and a surface active agent of the general formula in which A represents a trivalent polynuclear radical containing Patented Jan. 9, 1968 ICC at least 2 fused aromatic rings optionally substituted by chlorine but unsubstituted by alkyl groups,

X represents x being an integer from 1 to and preferably from 4 to 20,

n is zero or a number greater than zero, and

R represents hydrogen or a monovalent hydrocarbon radical containing up to 6 carbon atoms.

The surface active agents used in the compositions of our invention are obtained as described in copending US. patent application No. 344,553. Especially suitable surface active agents are those obtained by condensing formaldehyde or paraform in presence of a strong mineral acid with a reaction product of uor ,B-naphthol with from 4 to 30 moles of ethylene oxide. Such compounds have the above general formula in which A represents a naphthalene nucleus, X represents and R represents hydrogen. A particular example of such a surface active agent is the product obtained as described in Example 3 of the above copending application by condensing fi-naphthol with 15 moles of ethylene oxide and condensing the product with paraform.

Preferably a proportion of a liquid hydroxylated organic compound such as a glycol or diglycol is added to the mixture, propylene glycol solvents such as monopropylene glycol, dipropylene glycol, tripropylene glycol or mixtures of two or more of these glycols being preferred. Particularly suitable are mixtures of a major proportion by weight of a dipropylene glycol With a minor proportion by weight of monopropylene glycol. Homogeneous liquid compositions may be obtained by the use of such solvents.

Certain of the liquid compositions of our invention have the further advantage that they remain fluid and readily pourable down to quite low temperatures. This is particularly important since in some acid pickling plants in which acid pickling restrainers are used it is not always possible to store them in heated conditions in cold weather.

The amount of the composition which is added to the acid pickling bath may be varied over wide limits but We prefer to add between 0.01% and 0.5% of the composition calculated on the weight of 100% acid. Thus in the case of sulphuric acid we prefer to add between 0.15 lb. and 8 lb. of the composition per ton of 76% sulphuric acid (B.O.V.) in the acid pickling liquors. The concentration of sulphuric acid in the acid pickling liquors is usually between 2% and 25% by weight. Especially suitable proportions by weight of the constituents of the mixture are- Parts by weight Di-n-butylthiourea 1 Surface active agent 1-9 Liquid hydroxylated organic compound 0-8 The mixtures may be made by simple mixing of the ingredients optionally with the application of heat.

In addition to the ingredients referred to above other materials such as diluents and colouring matters may be added if desired.

The products are excellent corrosion restrainers in acid pickling and have little tendency to foam.

The invention is illustrated by the following examples- Example 1 A mixture of parts by weight of di-n-butylthiourea and 20 parts by weight of a [3-naphthol/l5 moles ethylene oxide/formaldehyde condensate prepared according to Example 3 of US. patent application No. 344,553 was dissolved in 70 parts by weight of dipropylene glycol. The product was a viscous liquid.

Example 2 A 40 cm. length of degreased bright-annealed mild meric surface active agent in which the basic monomer unit has the formula where A and X have the same meaning above, said com- Steel p, 6 Wide and thick, Was immersed 20 position containing from 1 to 9 parts by weight of surface in 20% WL/Wtaqueous Sulphuric acid Containing 002% active agent for each part by weight of di-n-butylthiourea. wt./wt. of the composition of Example 1 for minutes 2 The corrosion restraining composition f l i 1 at and was found to have lost 0-0400 gram in wherein the surface active agent R represents a hydrogen weight. A similar degreased mild steel strip treated under atom eXflcfly the 531716 Conditions with aqueous Sulphuric Z5 3. The corrosion restraining composition of claim 1 acid omitting the Composition of Example 1 Was found wherein in the surface active agent x has the value of to have lost 13500 grams in Weight 14 and R represents a hydrogen atom.

4. The corrosion restraining composition of claim 1 E l 3 which contains a liquid hydroxylated organic compound selected from the group consisting of monopropylene glycol, The following table gives the percentage loss of weight dipropylene glycol, tripropylene glycol and mixtures of of descaled mild steel strip (columns IV to VII) which at least two of these glycols, said composition containing has been immersed at a given temperature (column II) up to 8 parts by weight of said liquid hydroxylated organic for a given time (column III) in a sulphuric acid pickling compound for each part by weight of di-n-butylthiourea. bath of a given acid strength (column I: expressed as a 5. The corrosion restraining composition of claim 4 percentage Weight/weight of 76% sulphuric acid) and wherein the glycol is propylene glycol and the diglycol containing either no corrosion restraining composition is dipropylene glycol. (column IV) or the amounts of the corrosion restraining 6. A corrosion restraining composition of claim 1 which composition of Example 1 indicated in the heading of comprises a mixture of about 10 parts by Weight of columns V, VI and VII. di-n-butylthiourea and about 20 parts by weight of said Aeration of the aqueous acid solutions containing the corrosion restraining composition did not give rise to stable foams.

Example 4 The B-naphthol/ 15 moles ethylene oxide/ formaldehyde condensate used to prepare the composition of Example 1 was prepared as follows 100 parts of the condensate of p-naphthol with 15 moles of ethylene oxide were stirred whilst 4 parts of paraform and 2.26 parts of sulphuric acid were added. The mixture was stirred for 16 hours at 95 C., cooled and the sulphuric acid neutralised with 5 parts of triethanolamine. Triethanolamine sulphate formed a lower liquid layer which was separated from the upper liquid product layer.

What we claim is:

1. A corrosion restraining composition Which consists essentially of a mixture of di-n-butylthiourea and a polypolymeric surface active agent wherein x has the value of 14 dissolved in about 70 parts by weight of dipropylene glycol.

7. An acid pickling bath for ferrous metals consisting of an aqueous acid selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid and sulphamic acid containing from 0.01% to 0.5% of the composition of claim 1 calculated on the weight of r acid.

8. The acid pickling bath of claim 7 in which the aqueous acid is 2% to 25% sulphuric acid by weight.

9. An acid pickling bath for ferrous metals consisting of an aqueous acid selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid and sulphamic acid containing from 0.01% to 0.5% of the composition of claim 4- calculated on the weight of 100% acid.

It). The acid pickling bath of claim 9 in which the aqueous acid is 2% to 25% sulphuric acid by weight.

ing composition present in the bath being between 0.5 lb.

and 8 lb. per ton of 76% sulphuric acid present No references cited.

LEON D. ROSDOL, Primary Examiner.

S. D. SCHNEIDER, Assistant Examiner. 

